I'm taking Developmentor Web Services class this week. I'm fine with the basics, and I really don't need the class, however I'm getting a lot from it. There are a relatively small number of devs who are really into the core low level goo of WSDL, XSD, WS-XYZ etc. I'm not one of those developers. Fortunately our instructor is one of those guys that study all of the W3C and WS-xyz specs in earnest. I'm learning a lot interesting and some of it useful info. So far the class has been A+.
Today I wrote my first HTTP handler. It is surely a whole lot easier than writing ISAPI extensions. I think that I had something like 1 or 2 times in my life where I really needed to write an extension or filter. My experience has been that there are very very few times that something like this trick will be useful in your typical Enterprise application. But it is still fun to know about, play around with, and keep in the bag of tricks.